Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 121958
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
358 PM EDT SAT JUL 12 2014

.SHORT TERM...THIS AFTERNOON AND TONIGHT

RUC BASED MESOANALYSIS HAS BEEN CONFIRMING THE VALIDITY OF THE THE
EARLIER OUTPUT FROM THE IN-HOUSE HIRES ENSEMBLE...WITH REGARDS TO
THE LOCATION OF THE INSTABILITY GRADIENTS OVER LOWER MICHIGAN.
POOLED SURFACE MOISTURE CONTENT WITHIN THE LEE OF LAKE MICHIGAN HAS
RESULTED IN SBCAPES OF 500-1000 J/KG. EXPECT THE ONGOING ACTIVITY ON
THE LOCAL AND MOSAIC RADAR TO GENERALLY WEAKEN AS IT DETACHES FROM
INSTABILITY AND PUSHES EASTWARD INTO THE DTX CWA. WITH THAT
SAID...THE POTENTIAL FOR A SHOWER OR THUNDERSTORM WILL EXIST ANYTIME
FROM 22-03Z AS A VERY STRONG WARM AIR/THETA E ADVECTION PUSH WILL
ARRIVE AND PASS THROUGH THE AREA. THE LARGE SCALE FORCING MECHANISM
IS NOT A PRISTINE ONE...HOWEVER...AS THIS WARM AIR ADVECTION WILL BE
OCCURRING DIRECTLY INSIDE OF AN AMPLIFYING SHORTWAVE RIDGE.

FOR TONIGHT...THE DYNAMIC UPPER LEVEL CLOSED LOW AND NEGATIVE PV
ANOMALY THAT HAS BEEN GARNERING SO MUCH RECENT ATTENTION WILL SETTLE
SOUTHWARD TO PORTIONS OF THE UPPER PENINSULA AND LAKE SUPERIOR BY
12Z SUNDAY. WITH THIS FEATURE GETTING CLOSER...SOUTHEASTERN MICHIGAN
WILL BE IN A MORE FAVORABLE LOCATION TO BECOME INFLUENCED BY THE
RESURGENT NOCTURNAL LOW LEVEL JET. INCREASING MOISTURE
TRANSPORT...CONVERGENCE TIED TO THIS MIDLEVEL JET ENERGY WILL LEAD
TO A MORE PURE ELEVATED MIXED LAYER TONIGHT AND CATEGORICAL CHANCES
FOR SHOWERS AND THUNDERSTORMS. TIMING IS STILL A QUESTION MARK...BUT
REFINED TIMING TO THE WINDOW OF ROUGHLY 3-10Z...NORTH TO SOUTH. FOR
QPF PLACEMENT...FAVOR A GFS AND ECMWF SOLUTION WHICH IS DISPLACED
SLIGHTLY NORTH OF THE NAM (CENTERED PRIMARILY OVER THE HEART OF THE
CWA). THE NAM APPEARS TO SUFFER FROM SOME CONTAMINATION OF A
CONVECTIVE FEEDBACK LIKE RESPONSE CAUSING SOME MAJOR ISSUES IN THE
LOW LEVEL KINEMATIC FIELDS. THERE ARE HINTS IN THE MODEL SOLUTION
THAT THE MIDLEVEL JET AXIS DEVELOPING WILL BE FAIRLY DEEP...INVOKING
ORGANIZATION TO THE COOL SIDE DEFORMATION. THIS SHOULD RESULT IN THE
STREAMLINING OF UPSTREAM IOWA THUNDERSTORM ACTIVITY...DIRECTING IT
RIGHT INTO THE FORECAST AREA. FOR THIS REASON...WENT FAIRLY STOUT
WITH QPF AMOUNTS...UPWARDS OF AN INCH POSSIBLE. LACK OF TRUE
TROPICAL AIRMASS AND PROGRESSIVE BEHAVIOR OF CONVECTIVE COMPLEX DID
NOT WANT TO GO AGGRESSIVE WITH ANY HEAVY RAINFALL WORDING IN THE
ZONES. THAT CAN BE MORE OF A NOWCAST CONCERN. ELEVATED INSTABILITY
OF LESS THAN 1000 J/KG LIMITS THE POTENTIAL FOR SEVERE THUNDERSTORM
RISK OVERNIGHT.

&&

.LONG TERM...

LARGE CLOSED CIRCULATION WITH SIGNIFICANT EMBEDDED SHORTWAVES IS
NOTED ON WV IMAGERY MIGRATING SOUTHEAST ACROSS NORTHERN MANITOBA
THIS AFTERNOON. INITIAL HEIGHT FALLS ARE ALREADY EASING INTO THE
GREAT LAKES AND WILL ONLY INCREASE IN MAGNITUDE SUNDAY THROUGH
MONDAY AS THE POTENT VORTMAX OVER HUDSON BAY IS WHIPPED AROUND THE
LOW DRIVING THE CENTER OF THE CIRCULATION SOUTHWARD TOWARD THE
CENTRAL GREAT LAKES MONDAY INTO TUESDAY.

WITH H85 TEMPERATURES NEAR 15C TO BEGIN THE DAY AND SURFACE
DEWPOINTS NEAR 70, SUNDAY WILL QUALIFY AS A TYPICAL SUMMER DAY.
GIVEN EXPECTED RAINFALL TONIGHT, BOUNDARY LAYER MOISTURE WILL BE
PLENTY SUPPORTIVE OF A FAIR COVERAGE OF DIURNAL CU WHILE HIGHS CLIMB
TO AROUND 80 DEGREES. NOTICEABLY DRIER AIR WILL PUSH INTO THE REGION
DURING SUNDAY NIGHT ALONG THE PERIPHERY OF THE STRONGER HEIGHT
FALLS. THIS TREND WILL CONTINUE INTO MONDAY AS H85 TEMPS CONTINUE
THEIR GRADUAL DESCENT TOWARD 11C WHILE SURFACE TDS FALL INTO THE
MID/UPPER 50S. SIGNIFICANT MID-LEVEL DRY AIR WILL REALLY LIMIT
PRECIP POTENTIAL ON SUNDAY. BY MONDAY, FORCING MAY BE SUFFICIENT TO
GENERATE A FEW SHOWERS, BUT AT THIS POINT IT SEEMS THAT EVEN THE
FORECAST 30 POP, WHICH CONTINUES THE RECENT TREND OF BEING MORE
CONSERVATIVE FOR MONDAY, IS BEING GENEROUS. INSTEAD, PREFER TO
CHARACTERIZE MONDAY AS A COOLER, DRIER, AND MOSTLY CLOUDY DAY AS
DIURNAL CU DEVELOPMENT SHOULD BE EXPANSIVE OWING TO STEEPING LAPSE
RATES.

BY MONDAY NIGHT, SIGNIFICANT HEIGHT FALLS ON THE ORDER OF 1DM/HR
WILL BE PUSHING INTO THE AREA ON THE LEAD EDGE OF THE ENCROACHING
HIGH-LATITUDE CIRCULATION. MID-LEVELS WILL REMAIN RATHER DRY DURING
THIS TIME, AND PWATS ARE FORECAST TO REMAIN SOLIDLY BELOW 1 INCH
THROUGH MONDAY NIGHT. HOWEVER, INCREASINGLY STRONG LARGE SCALE
FORCING SEEMS ENOUGH TO WARRANT AT LEAST A HIGH CHC POP ACROSS MUCH
OF THE AREA DURING THE MONDAY NIGHT PERIOD, PARTICULARLY ACROSS THE
SOUTHEAST WHERE BETTER QUALITY MOISTURE RETURN CAN BE EXPECTED.

THE TUESDAY THROUGH FRIDAY FORECAST PERIOD WILL CONTINUE TO BE
INFLUENCED BY THE LARGE UPPER LOW THAT WILL BE OVER THE CENTRAL
GREAT LAKES ON TUESDAY BEFORE SHIFTING OFF TO THE EAST BY THE END OF
THE WEEK. WITH THE UPPER LEVEL TROUGH DIGGING ACROSS THE AREA THIS
WILL BRING CHANCES FOR PRECIPITATION THROUGH AT LEAST THURSDAY
BEFORE THE TROUGH EXITS AS HIGH PRESSURE AND UPPER LEVEL RIDGING
START BUILDING IN. NORTHWESTERLY FLOW IN ASSOCIATION WITH THE TROUGH
WILL BRING IN COOLER TEMPS ON TUESDAY WITH HIGHS STRUGGLING TO REACH
70 AND WILL NOT BE HELPED WITH THE BREEZY CONDITIONS DUE TO THE
TIGHTENING PRESSURE GRADIENT.  OVERALL CONDITIONS DO START TO
IMPROVE SOMEWHAT TOWARDS THE END OF THE WEEK AS HIGHS CLIMB BACK
CLOSER TO NORMAL.

&&

.MARINE...

THE PRIMARY MARINE HAZARD THROUGH THE WEEKEND WILL BE WIDESPREAD
THUNDERSTORMS TONIGHT...ESPECIALLY FOR CENTRAL LAKE HURON AND POINTS
SOUTH INCLUDING LAKES SAINT CLAIR AND ERIE. OTHERWISE...WINDS WILL
REMAIN LIGHT TO MODERATE AND ARE EXPECTED TO REMAIN WELL BELOW SMALL
CRAFT ADVISORY CRITERIA. A COLD LOW PRESSURE SYSTEM WILL MOVE INTO
THE GREAT LAKES TUESDAY INTO WEDNESDAY. WEST WINDS WILL GUST TO NEAR
20 KNOTS DURING THIS TIME. IN ADDITION...WATERSPOUTS WILL BE LIKELY
OVER AREAS OF WARMER WATER BEGINNING MONDAY NIGHT. AREAS MOST AT
RISK FOR WATERSPOUTS FROM MONDAY NIGHT THROUGH WEDNESDAY NIGHT
INCLUDE SOUTHERN HALF OF LAKE HURON...LAKE SAINT CLAIR...AND THE
MICHIGAN WATERS OF LAKE ERIE.

&&

.AVIATION...ISSUED 156 PM EDT SAT JUL 12 2014

//DISCUSSION...

VFR CONDITIONS WILL HOLD THROUGHOUT THE AFTERNOON HOURS AS RIDGING
HOLDS TIGHT OVER SOUTHEASTERN MICHIGAN. FOCUS FOR THIS SET OF TAFS
WAS TO REFINE TIMING OF PRECIPITATION AND THUNDERSTORMS. QUITE A BIT
OF UNCERTAINTY REMAINS. FIRST THING TO WATCH FOR WILL BE SHOWER
ACTIVITY POSSIBLY RELEASING OFF OF THE LEE OF LAKE MICHIGAN SURFACE
TROUGH...MAKING A RUN FOR THE TRI CITIES LATE THIS AFTERNOON. IN
ADDITION...LEAD PUSH OF WARM AIR ADVECTION WILL LEAD TO A LOW CHANCE
FOR A SHOWER OR THUNDERSTORM JUST ABOUT ANYWHERE OVER SOUTHEASTERN
MICHIGAN DURING THE SAME TIME. CONFIDENCE REMAINS TOO LOW TO INCLUDE
IN FORECAST. BEST FORCING AND POTENTIAL FOR SHOWERS AND
THUNDERSTORMS WILL COME LATER TONIGHT AS UPPER LEVEL FORCING FINALLY
SETTLE INTO THE REGION. THERE REMAINS SOME TIMING DIFFERENCES...BUT
A COUPLE OF HOURS. LATEST FEELING IS THAT MAJORITY OF UPSTREAM
CONVECTION WILL SLIDE THROUGH SOUTHEASTERN MICHIGAN BETWEEN 5-10Z.
THE THUNDERSTORM ACTIVITY IS EXPECTED TO BEGIN ACROSS THE SAGINAW
VALLEY...THEN SETTLE SOUTHWARD TOWARDS THE OHIO/MICHIGAN BORDER.

//DTW THRESHOLD THREATS...

* THERE IS HIGH CONFIDENCE THAT THUNDERSTORMS WILL OCCUR OVERNIGHT.

* THERE IS HIGH CONFIDENCE THAT CEILINGS WILL FALL BELOW 5000 FT
OVERNIGHT.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LAKE HURON...NONE.
LAKE ST CLAIR...NONE.
MI WATERS OF LAKE ERIE...NONE.

&&

$$

SHORT TERM...CB
LONG TERM....JVC/SS
MARINE.......JVC
AVIATION.....CB


YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE
AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).





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